Objective Lens Tilt Control for Multilayer Optical Disc Aberration
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Solution Overview
Problem
Conventional optical disc devices face challenges in accurately recording and reproducing information from multilayer optical discs with three or more information recording surfaces, due to varying light transmissive layer thicknesses, which result in significant third-order spherical and coma aberrations, leading to instability in optical head performance.
Innovation Solution
An optical disc device with a light source, objective lens, spherical aberration correcting section, lens tilting section, and tilt detecting section, where the objective lens is tilted based on specific mathematical expressions to optimize wavefront aberration correction, ensuring proper alignment and focus across different light transmissive layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a multilayer structure of information recording surfaces is formed with different light transmissive layer thicknesses, then the capacity of the optical disc is increased, but third-order spherical aberration is generated on information recording surfaces with non-optimum layer thicknesses
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the tilt angle of the objective lens based on the detected thickness of the light transmissive layer. The control unit modifies the tilt angle parameter in response to aberration detection, allowing the optical system to adapt to different layer thicknesses and minimize spherical aberration while maintaining high disc capacity through multilayer structures.
2Quantity of substance
If the thickness of the light transmissive layer is displaced from the optimum thickness, then the capacity of the optical disc is increased, but the aberration amount of third-order spherical aberration increases
Solution Approach 1:
The patent implements feedback by using an aberration detection unit to measure the actual third-order spherical aberration on the information recording surface. The control unit then uses this feedback information to adjust the tilt angle of the objective lens, creating a closed-loop system that continuously optimizes the optical path and compensates for aberrations caused by non-optimum layer thicknesses.
Solution Approach 2:
The system dynamically changes the tilt angle parameter of the objective lens based on real-time aberration detection. By adjusting this optical parameter in response to detected thickness variations, the system maintains optimal focus and minimizes spherical aberration while supporting increased disc capacity through thicker or varied light transmissive layers.
3Manufacturing precision
If spherical aberration is corrected depending on the thickness of the light transmissive layers, then the recording and reproduction accuracy is improved, but the aberration amount of third-order coma aberration resulting from disc tilt and lens tilt changes
Solution Approach 1:
The patent applies dynamics by making the tilt angle of the objective lens adjustable rather than fixed. The control unit dynamically modifies the tilt angle based on the specific thickness of the light transmissive layer and the detected aberration characteristics. This dynamic adjustment allows the system to optimize for spherical aberration correction at each layer while managing the resulting changes in coma aberration through adaptive control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables stable and accurate recording and reproduction of information across multilayer optical discs with varying light transmissive layer thicknesses, minimizing wavefront aberrations and maintaining optimal performance within the Marechal criterion.
Implementation Method 1
an objective lens which converges the laser light emitted from the light source on a predetermined one of the information recording surfaces of the information recording medium
Implementation Method 2
a spherical aberration correcting section which corrects a spherical aberration resulting from the thickness of the respective light transmissive layers of the information recording medium
Implementation Method 3
a lens tilting section which tilts the objective lens in a radial direction of the information recording medium
Implementation Method 4
a tilt detecting section which detects a tilt of the information recording medium in the radial direction
Data Source
AI summary
An object of the invention is to provide an optical disc device, an optical head, and an information processing device that enable to advantageously record or reproduce information with respect to an information recording medium having three or more information recording surfaces with light transmissive layers of different thicknesses from each other. Assuming that an aberration amount of third-order coma aberration resulting from tilting a multilayer optical disc (60) by a unit angle is CMD0 (unit: mlambda/deg), an aberration amount of third-order coma aberration resulting from tilting an objective lens (8) by a unit angle is CML0 (unit: mlambda/deg), a tilt angle of the multilayer optical disc (60) is theta, a coefficient is k0, and a tilt angle of the objective lens (8) by an objective lens actuator (9) is alpha0 in converging laser light on an information recording surface having a largest light transmissive layer thickness out of the information recording surfaces of the multilayer optical disc (60), the objective lens actuator (9) tilts the objective lens (8) in such a manner that the tilt angle alpha0 of the objective lens (8) satisfies the following mathematical expression: alpha0=theta×k0×CMD0/CML0, where 0.5<k0<0.9.